Comprehensive transthoracic echocardiography, 12-lead ECG, biomarkers and Holter monitoring will be performed at the time of randomization and at 6 and 12 months, respectively. Blood samples and ECG will be collected one week after the onset of treatment, and subsequently at 1, 2,3,6,9 and 12 months. During this period of 12 months, all patients will be followed for recurrence of symptomatic AF. Any relapse of symptomatic arrhythmia should be documented, if possible by 12-lead ECG or Holter monitoring. Only documented AF-recurrence by 12-lead ECG or Holter monitoring will be taken into account. CMR exams will be preformed at baseline and at 12 months, respectively.